Steam plant



w. T. HEDLUND Aug. 2s, 192s.

STEAM PLANT Filed Sept. 2, 1925 .2 Sheets-Sheet l Aug. 28, 1928.1,682,674

W. T. HEDLUND STEAM PLANT Filed Sept. 2, 1925 2 Sheets-Sheet 2 IN ENTOI? Patented Aug. 28, 1928.

,i UNITED STATES WILLIAM THEODORE HEDLUND, 0F NEW YORK, N. Y.

STEAM ILLNT.

.Application led September 2, 1925. Serial No. 54,096.

The invention consists in several novel features of steam plantarrangement and control and has among its objects: to provide a novelsteam plant; to extract the maximum amount of heat from products ofcombustion to regulate feed heating in response to temperature; torovide a novel accumulator plant; to provi e a wholly automatic controlfor an accumulator plant; to circulate cold water and accumulated hotwater through the same feed preheater; to mix cold and hot water iiiaccordance with temperature changes for supply to a boiler; and otherobjects which will e apparent from the following description. A newmethod of heating and control is also included. i

Description of the invention is given with references to theaccompanying drawings in which: Fig. 1 shows one modification of theinvention and Fig. 2 a second modification thereof.

Referring more particularly to Fig. 1, 1.0 designates the steam drum ofa boiler which is supplied with feed water through feed conduit 11. Theflow of feed through conduit 11 is controlled in any manner. As an examle, I have shown an expansible tube 12 fixe at its lower end to astationary frame 13, and, at

its upper end, movable with respect to the frame.- Tube 12 is connectedby means of tubes 14 and 15 with the steam and water spaces of drinn 10.The free end of tube 12 operates a feed valve 16 through a chain 17, soas to maintain the water level within fixed limits. This feed 'l controlmechanism is known pen se wherefore its operation need not be explained.

The Yfeed is preheated in economizer 18 which may be any type offeed'water heater. The economizer is heated by means of the fine gases ofthe boiler which pass from the boiler and through the waste gas flue 95in the mannei' indicated by arrows. Water is supplied to conduit 11through conduitV 19 from the eeonomizer. More feed water flows throughconduit 19 than is needed in eonduit'll and the remainder flows throughconduit 21 to accumulator 20. Flow through conduit 21 is controlled byan overflow valve 22 for which purpose any of various known types ofoveriow valves may be used. The overflow valve operates to increase itsfiow area upon increase ci pressure in front of the same and decreaseits flow area upon decrease of pressure in front of the same. therebyholding the pressure in front of the saine Substantially constant. Inthe form illustrated the overflow valve comprises a diaphragm 102forming one side of a chamber 103 in which steam pressure acts through'tube 104. Pressure in chamber 103 is balanced by a spring 105.

Econor'nizer 18 is supplied with Water by means of centrifugal ump 23,which is operated at constant speed3 by means of an electric motor 24.

The pump receives its sup ly partly from accumulator 20 and partly roman outside source of cold water 25.

Steam generated in the boiler flows through conduit 26, which suppliessteam consumers of' any kind, for example turbine 27. Steam is generatedat a rate sometimes greater than the rate of consumption, the surplusbeing conducted to the accumulator. In the present instance, this isdone by means of conduit 28 containing an overflow valve 29 which oerates to hold a constant pressure of supp y for the turbine. Conduit 28discharges steam into the accumulator where it is condensed and thewater thus formed iseither regenerated to supply low pressure steamconsumers such as the low pressure section ofthe turbine, or passesagain through the economizer.

.107 designates a hot water consumer supplied with water fromaccumulator 20 through conduit 106.

The relative amount of water taken by pump 23 from accumulator 20 andsource 25 is controlled in such a manner that the greatest possibleamount of heat is extracted from the flue gases so that the highesteiiiciency of the boiler may be obtained. To ci'ect'this purpose adevice responsive to temperature is placed in the path of flue gasesjust beyond the economizer and is connected with control elementsdetermining the relative supply of cold and hot water so that a constantlow temperature of the fiue gases leavin the steam generating plant isobtained. T e illustration of the temperature responsive device in Fig.l, which like other parts is diagrammatic, but sufficient to be entirelyclear to those skilled in the art to which the invention belongs, showstwo elements 30 and 31 which have different cci-efficients of expanJsion, connected between a fixed standard 32 and a lever 33. Element 30has a greater rate of expansion than element 31. To lever 33 is attacheda baliling member 34 which controls outiow of a premura fiuid such asair or water from a conduit 35. Valve 43 in conduit 35 is normally wideopen and can :for

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the moment be left out of consideration. Conduit 35 connects withchambers in two regulators of which one controls a valve 36 in coldwater supply line 37 and the other controls a valve 38 in theaccumulator water discharge line 40. Valve 36 is cont-rolled by movementof a piston 41, on the one side or' which fluid pressure acts in chamber42 and on the ,other side of which a spring 44 acts. The arrangement issuch that increase of pressure in chamber 42 causes closing of the valveports. Valve 38 is controlled by movement of a piston 45 on the one sideof which fluid pressure acts in chamber 46 and on the other side ofwhich a spring 47 acts. The arrangement is such that increase ofpressure in chamber 46 causes opening of the valve ports. It is thusseen that the action of valves 36 and 38 might be termed reciprocalsince when one opens the other closes. Conduit 48 supplies Huid underpressure to both chambers 42 and 46, the supply to chamber 42 beingpartly effected through branch conduit 108 extending between conduits 48and 35. In conduit 48 is a restriction 49 shown as a hand valve whichpermits variance of outow from conduit 35 to eifect changes of pressurein chambers 42 and 46.

In operation: Suppose the temperature of the Hue gases increases.Element 30 being more expansible than element 31, lever 33 is rocked inanti-cloclrwise direction and baffling member 34 is moved further awayfrom the end of conduit 35 so that a greater outflow of pressure fluidtakes place. Due to restriction 49, this causes a lowering of pressurein chamber 42 and a. lowering of pres# sure in chamber 46. Springs 44and 47 then have a greater force than the iuid force on their respectivepistons and valve 36 1s opened more or less and valve 38 is closed moreor less, thus increasing the supply of cold water to pump 23 anddecreasing the supply of hot water from the accumulator. The waterleaving pump 23 is then of lower temperature and on passing through theecon= omizer reduces the temperature of the flue gases to the desirednormal value.

It is to be seen that, in the arrangement shown. all the water oftheaccumulator plant circulates through the same economizer, thus affordinga smaller plant than 'if two economizers are used. one for supplyingfeed and one for circulating water from the accumulator through {iuegases and back to the accumulator, while the Hue gases are run down toan eiiciently low exit temperature at all times and hot water issupplied to the boiler at all times so that substantially onlyevaporation need take place in the boiler. Since there is a surplus iowot water through the economizer over the boiler feed water demand. steamformation in the economizer is prevented and a long life of theeconomizer is possible.

A further feature of the present invention includes regulationresponsive to low and high water levels in the accumulator. This featurecomprises means to close valve 36 when the water level in theaccumulator rises above a predetermined value regardless of the factthat the temperature control may tend to open the valve and means toopen valve 36 wide when the water level in the accumulator falls below apredetermined low value regardless of a tendency of the temperaturecontrol to close the valve. To illustrate a fomi of the rst means, thereis shown a float box 50 connected to the inside of the accumulatorthrough conduits 51 and 52 and containing within the saine a float 53which normally rests in lowered position. To float 53 is connected a pin54, having a head 55 on the same which is adapted to Contact a head 56on upward movement of the float. Head 56 is attached to a lever 57pivoted at 58. Lever 57 operates a valve 59, normally held closed by aspring 60, and situated in a pipe 61 branched off from pipe 48,preferably ahead of restriction 49, and leading to a chamber 62 on oneside of a piston 63, the opposed side of which is subject to the forceof spring 64. Piston 63 controls valve 43. Valve 59 being normallyclosed, valve 43 is normally lppen under the action of spring 64. 65designates a very minute opening leading from chamber 62 to assure anopening of valve 43 at all times except when valve 59 is open.

In operation: if the water level in the ac cumulator rises to such aheight that float 53 is lifted, head contacts with head 56 and moves thesame upwardly, thereby rocking lever 57 so that its left hand end, asshown, is moved downwardly and valve 59 is opened. Communication is thenestablished between conduit 43 and chamber 62.' This causes a downwardmovement et piston 63 and a closing of valve 43. Closure of valve 43causes increase ot pressure in chamber 42 whereby ,valve 36 is closed.Simultaneously valve 38 is opened wide due to the increase of pressurein conduits 106 and 48 and consequently in chamber 46. rlhus the outsidesupply of water is cut off and the supply of water from the accumulatorto the economizer will reduce the water level in the accumulator tobelow the predetermined high value at which float 53 rises. Upondecrease of water level, valve 59 closes, valve 43 opens and the controlis again responsive to flue gas temperature.

The low water level control device. in the illustrated form, comprises afloat box connected to the inside of the accumulator through conduits 66and 67. Within float box 65 is a float 68, normally held in liftedposition since the water level in the accumulator is usually higher thanthe float box 65. In lifted position an extension 69 on the float, whichprojects through the float box. holds the open end of a pipe 70 closed.Pipe 70 so low that float 68 is lowered and opens the end of conduit 70,a releaseo'f fluid pressure occurs in conduit 48 whereby fluid pressureis released in chambers 42 and 46 and valve 36 opens wide and valve 38closes so that a relatively large amount of cold water is supplied tothe system to make up the reserve. This supply of water is independentof the control in response to temperature.

As is obvious,-various changes in arrangement and various substitutionsare possi) within the scopeoi. the invention. In certain cases the valve38'may be omitted and the whole system will work quite as well. It mightbe desired in such case to place a check valve opening away from theaccumulator in place of valve 38.

In the modification shown in Fig. 2, the steam generating unit is in theform of an indirectly heated boiler comprising a primary section 72 inwhich the vapor of a special heat transfer medium is vaporized and asecondary section in the form of a coil 7 3 in which steam is generatedmore or less in accordance with demand, at a rate which may differ fromthe rate of combustion.

Feed water is supplied to the coil 7 3 from economizer 18 throughconduits 19 and 11, as in the previously ldescribed moditication. Theeconomizer is in this case also heated by llue gases. More water passesthrough the economizer than passes to the boiler, that not being neededby the boiler (as that amount is determined by constant pressure inconduit 19) passing through overflow valve 22 and into accumulator 20;

Supply of feed water to coil 7 3 is controlled by a valve 74 operated bysteam pressure 1n conduit 7 5, which latter conduit is connected to thesteam end of coil 7 3. Steam pressure in conduit 75 is a function of thesteam de mand and since feed water is to be supplied in accordance withsteam demand, variations in pressure in conduit 75 can be used todetermine the feed supply. When pressure in conduit 75 drops, pressurealso drops 1n chamber 76 on one side of diaphragm 7 .at tached to thespindle of valve 74 and spring 78 causes movement of the valve toincrease the feed supply. Conversely, rise of pressure' causes adecrease of feed supply. 1

Supply of feed Water to economizer 18 takes place through two conduits79 and 80. Conduit 79 has itssource in accumulator 2O and includes acentrifugal pump 81 driven by a steam turbine 82. Turbine 82 is suppliedwith steam from conduit 75 through con duit 83. In conduit 88 is a valve84 actuated by variations of pressure in conduit 7 5 1n such a mannerthat increase of pressure causes a decrease of flow through the valve.In the form illustrated, steam pressure acts through in steamgeneration.

conduit 85 on diaphragm 86, opposed to which is the force of a spring87.

Conduit 80 connects with the discharge of a pump 88. Pump 88 is suppliedwith cold water, as, for example, from a reservoir 89 supplied throughconduit 90, flow through which is controlled by float 91 to maintain aconstant level in reservoir 89.y Pump 88 is driven by turbine 92supplied with steam from conduit 75 through conduit 93. Flow throughconduit 93 and consequently the speed of the turbo-pump unit iscontrolled by valve 94. Valve 94 is controlled in such a manner that ittends to maintain a constant temperature of lue gases in liuc 95.

In the form illustrated, the means for effecting this control comprisesa bulb 96 filled with volatile liquid and connected with a chamber 97,on one side of which is a diaphragm 98, through tube 99.` Diaphragm 98is connected to operate valve 94. In operation ;y if the temperature influe increases in the vicinity of thermostatic bulb 96, an expansion ofliquid in the bulb takes place which causes movement of diaphragm 98 sothat valve 94 is opened more or less and more steam is Supplied toturbine 92 so that the speed of pump 88 is increased and more cold wateris supplied to the economizer whereby the temperature of the flue gasesis returned to its normal low value.

Assume that the increase in temperature of flue gases was due to amomentary decrease Decrease in. steam generation (other conditions beingunchanged) results in an increase of pressure in conduit 7 5 which.acting through conduit 85, causes diaphragm 86 to be flexed against theforce of spring 87 so that valve 84 isI closed and less hot Water passesfrom accumulator 20, through pump 81 and to the economizer. rlhe twosupply regulating devices thus cooperate to maintain a given low fluegas exit temperature.

Afsiudden increase in load results in a decrease of steam pressure inconduit 75 and an opening of valve 84 to supply more hot Water. At thesame time it causes a decrease ot furnace gas temperature wherebyvliquid in bulb 96, tube 99, and chamber 97 contracts and valve 94 closesthus decreasing or en-4 tirely cutting oil the supply or' cold water.

By means of conduit 101 and valve 102 therein, a certain amount oitsteam is always caused to byv-pass valve 84 so that a supply of Water tothe economizer is at all times assured. 5

designates a steam consumer sup lied 1from conduit 7 5, which consumermay e of any type.

Obviously various parts of the modifications shown in Figs.v 1 and 2 maybe interchanged and combined. n v

It isto be understood that showings of valves is diagrammatic and that,in practice,

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it is preferred to use more complicated valves with force multiplyingmeans which will give more sensitive action.

Obviously the use of two or more separate economizers will fall Withincertain phases of the invention.'

IVhat I claim is:

1. A feed Water heater adapted to he heated by a heating agency Withvalve mechanism to control flow through the same responsive totemperature of the heating agency and a boiler supplied with Water fromsaid feed Water heater.

2. In combination, a boiler, a waste gas flue therefor, a feed waterheater in said flue, means to supply cold Water to said heater, controlmeans for the first-mentioned means, a temperature responsive device insaid flue and means whereby the temperature responsive device operatesthe control means.

3. In combination, a boiler, a Waste gas flue therefor, a feed Waterheater in said flue, means to supply cold Water to said feed wat-erheater and means to control the supply means in accordance withvariations of temperature in said flue.

4. In a steam plant, in combination, a boiler, a feed water heatertherefor, means to supply cold water to said heater, means to supply hotwfater to said heater and automatic means responsive to variations ofplant load to control the relative amounts of cold and hot Watersupplied.

5. In combination, a boiler, a feed water heater therefor, means tosupply cold Water to said heater, means to supply hot Water to saidheater and means responsive to temperature of gases of combustion ofsaid boiler to determine the relative amount of cold and hot Watersupplied.

V6. In combination, a boiler, a Waste gas flue therefor, a feed waterheater in said flue, means to supply cold water to said heater, means tosupply hot water to said heater and means to control the relative supplyof cold and hot Water to maintain a constant temperature in said Wastegas flue.

7. In combination, a boiler, a Waste gas luethercfor, a feed Waterheater in said flue, means 'to supply cold Water to said heater, meansto supply hot water to said heater, control apparatus to regulate therelative amounts of cold and hot water supplied and a temperatureresponsive device situated in said tine in the path of gasestherethrough bevond the heater and operatively connected with saidcontrol apparatus.

8. In combination, a boiler, a feed Water heater, an accumulator, meansto conduct cold Water to the heater, means to conduct hot water from theaccumulator to the heater, means to conduct Water from the heater to theboiler and means to conduct Water from the heater to the accumulator.

9. In combination, a boiler, a feed water heater, an accumulator, meansto conduct cold Water to the heater, means to conduct hot water from theaccumulator to the heater, means to conduct Water from the heater to theboiler, means to conduct Water from the heater to the accumulator andmeans to control flow through the last-mentioned means to maintain aconstant exit pressure for the heater.

10. In a steam plant, in combination, a boiler, a feed water heatertherefor, means to supply cold water to said heater, an accumulator,means to supply hot water to said heater from said accumulatorI andautomatic means responsive to variations of plant load to control therelative amounts of hot and cold Water su plied.

11. In com mation, a boiler, a Waste s flue therefor, a fed Water heaterin said figlie, means to supply cold water to said heater, anaccumulator, means to supply hot water to said heater from saidaccumulator, means to conduct water from said heater to said boiler,means to conduct water from said heater to said accumulator and means tocontrol the relative supply of cold Water and hot Water to said heaterto maintain a constant temperature in said waste gas flue.

12. In combination, a boiler, a feed Water heater therefor, a source ofcold water, a cold water conduit conducting water from said source tosaid heater, an accumulator, a hot water conduit conducting hot waterfrom said accumulator to said heater, means to conduct Water from saidheater to said boiler, means to conduct water from said heater to saidaccumulator and means responsive to temperature of gases of combustionof said boiler to control the flow through the cold water conduit andthe hot water conduit.

13. In combination, a boiler, a feed water heater therefor, a source ofcold water, an accumulator, a pump, means to conduct water both fromsaid source and said accumulator to said pump, means to conduct Waterfrom said pump to said heater, means to conduct water from said heaterto said boiler and means to conduct Water from said heater to saidaccumulator.

14. In combination, a boiler, a feed water heater therefor, a source ofcold water, an accumulator, a pump, meansl to conduct Water both fromsaid source and said accumulator to said pump, means to conduct waterfrom said pump to said heater, means to conduct water from said heaterto said boiler, means to conduct Water from said heater to saidaccumulator and means to control the relative amounts of Water conductedfrom said source and said accumulator to said pump.

15. In combination, a boiler, a feed water heater therefor, a source ofcold Water, an accumulator, a pump, means to conduct Water both .fromsaid source and said accumulator to said pump, means to conduct waterfrom said pump to said heater, means to conduct Water from said heaterto said boiler, means to conduct Water from said heater to saidaccumulator and means responsive to temperature of gases of combustionto determine the relative amounts of Water conducted from said sourceand said accumulator to said pump.

16. In combination, a boiler, a feed Water heater therefor, anaccumulator, and means responsive to Water level in the accumulator tocontrol supply of Water to said feed water heater.

17. In combination, a boiler, a feed Water heater therefor, anaccumulator, means to supply cold water to said heater, means to conducthot Water from the accumulator to the heater, means to conduct Waterfrom the heater to the boiler, means to conduct Water from the heater tothe accumulator and means, normally inactive, operating upon rise ofwater level in said accumulator' above a predetermined value to decreasethe said supply of cold Water to said heater.

18. In combination, a boiler, a feed water heater therefor, anaccumulator, means to supply cold water to said heater, means to conducthot Water from the accumulator to the heater, means to conduct Waterfrom the heater to the boiler, means to conduct Water from the heater toe accumulator and means, normally inactive, operating upon lowering ofWater level in said accumulator below` a predetermined value to increasethe said supply of cold Water to said heater.

19. In combination, a boiler, a feed water heater therefor, anaccumulator, means to supply cold Water to said heater, means to conducthot Water from the accumulator to the heater, means to conduct Waterfrom the heater to the boiler, means to conduct Water from the heater tothe accumulator and means, normally inactive, operating upon rise ofWater level in said accumulator above a predetermined value to decreasethe said supply of cold Water to the said heater and means, normallyinactive, operating upon lowering of Water level in said accumulatorbelow a predetermined value to increase the said supply of cold water tosaid heater.

20. Apparatus as set out in claim 17 wherein the normally inactive meanscomprises a float, a main control member and fluid pressure operatedmeans to operate the main control member in response to movement of thefloat.

21. Apparatus as set out in claim 18 wherein the normally inactive meanscomprises a float, a main control member and .fluid pressure operatedmeans to operate the main control member in response to movement of thefloat. y

Q2. In combination, a boiler, a waste gas flue for said boiler, a feedWater heater in said flue, means to supply cold water to said heater, anaccumulator, means to supply hot water to said heater from saidaccumulator, means to conduct Water from said heater to said boiler,means to conduetwater from said heater to said accumulator, means,normally active, and responsive to temperature in said flue, to controlthe relative supply ofv cold and hot Water to said heater and means,normally inactive, operating upon rise of Water level in saidaccumulator above a predetermined value, to decrease the supply of coldWater to the heater.

23. In combination, a boiler, a Waste gas flue for said boiler, a feedWater heater in said flue, means to supply cold Water to said heater, anaccumulator, means to suppl hot Water to said heater from saidaccumulator, means to conduct Water from said heater to said boiler,means to conduct water from said heater to said accumulator, means,normally active, and responsive to temperature in said flue, to controlthe relative supplyof cold and hot water to said heater and means,normally inactive, operating upon lowering of water level in saidaccumulator below a predetermined value, to increase the supply of coldwater to the heater.

24. In combination, a boiler, a Waste gas flue for said boiler, a feedWater heater in said flue, means to supply cold Water to said heater, anaccumulator, means to supply hot water to said heater from saidaccumulator, means to conduct Water from said heater to said boiler,means to conduct water from said heater to said accumulator, means,normally active, and responsive to temperature in said flue, to controlthe relative supply of cold and hot water to said heater and means,normally inactive, operating upon rise of Water level in saidaccumulator above a predetermined high value, to decrease the supply ofcold water to the heater regardless of operation of the temperatureresponsive means and means, normally inactive, operating upon loweringof Water level in said accumulator below a predetermined'low value,totincrease the supply of cold Water to the heater regardless ofoperation of the temperature re sponsive means.

25. In combination, a boiler, feed preheat ing means therefor, means tosupply cold Water to the boiler through the feed preheating means, meansto supply hot Water to the boiler through the feed preheating means andcontrol apparatus responsive to temperature of gases of combustion ofsaid boiler to determine the relative amount of cold and hot Watersupplied.

26. In combination, a boiler, a Waste gas flue therefor, feed Waterpreheating means for said boiler situated in said flue, means to supplycold Water to said boiler through sai preheating means, an accumulator,means to supply hot Water to said boiler through said preheating meansand means re sponsive to temperature in said flue to control therelative supply of hot and cold Water.

27. The method of producing steam which comprises mixing hot water andcold water, heating the mixture, proportioning the relative amounts ofcold and hot water mixed so that the temperature of the heating agent isreduced to a denite amount and vaporizing the mixture.

28. The method of producing steam which comprises mixing cold Water andhot Water, vaporizing a portion of the mixed Water and storing theremainder in variable quantity for subsequent remixing.

'29. The method of producing steam which comprises mixing cold water andhot Water, heating the whole mixture, vaporizing a portion of themixture, storing the remaining unvaporized water in variable quantity,mixing the stored Water with cold water and again heatin the Wholemixture.

30. he method of producing steam which comprises mixing cold Water andhot Water, heatln f the Whole mixture, vaporizing a portion o themixture, storing the remaining unevaporated water for subsequentremixing and proportioning the relative amounts of cold water and hotwater mixed in accordance with temperature of the heating agent.,

31. The method of feeding a boiler which comprises introducing a mixtureof hot water and cold water into the boiler and controlling the relativesupply of components to the mixture in accordance with temperature ofgases of combustion leaving the boiler.

32. In combination, a boiler, a feed water heater, an accumulator, meansto supply Water to the heater, means to conduct Water from the heater tothe accumulator, means to conduct Water from the accumulator to theboiler and means responsive to temperature of gases of combustion of theboiler to control the Water supply.

33. In combination, a boiler, a feed Water heater, anaccumulator, meansto supply Water to the heater, means to conduct water from the heater tothe boiler, means to conduct water from the heater to the accumulator,means to conduct Water from the accumulator to the boiler, and means tocontrol flow from the heater to the accumulator to maintain a constantexit pressure for the heater.

34. In combination, a boiler, a feed water heater.

35.v In combination, a boiler, a feed Water heater, an accumulator,means to supply water to the heater, means to conduct water from theheater to the boiler, means to conduct Water from the heater to theaccumulator, means to conduct Water from the accumulator to the boiler,means to control flow from the heater to the accumulator to maintain aconstant exit pressure for the heater and means responsive totemperature of gases of combustion of the boiler to control the watersupply to the heater.

36. In combination, a boiler, a feed Water heater, an accumulator, meansto supply Water to the heater, means to conduct Water from the heater tothe boiler, means to con` duct Water from the heater to the accumulatorand means to conduct Water from the accumulator to the boiler,comprising, in part, the means to conduct water from the heater to theboiler 37. A boiler, a feed water heater, a feed water accumulator andconduits connecting the boiler, feed water heater and accumulator tosupply the boiler and accumulator in parallel from the feed water heaterand the boiler from the accumulator through the feed water heater.

38. The method of operating a boiler plant including a boiler, a feedWater heater and an accumulator which consists in withdraw ing steamfrom the boiler in accordance with steam demand, passing Water throughthe feed heater at a different rate than the rate of steam demand and atsuch rates that the flue gas temperature at the exit of the feed heateris constant, passing the surplus water discharged from the feed heaterinto the accumulator and storing the same for subsequent use by theboiler.

In'testimony whereof I ailix my signature.

WILLIAM THEODORE HEDLUND.

